Field of the Invention
The present invention relates generally to the flighted screws used in injection-molding, extrusion, and similar apparatus. More particularly, the present invention relates to improvements in such screws to increase their versatility by increasing the number of polymer formulations the screw is capable of optimally processing.
Summary of the Prior Art
In injection-molding and extrusion of polymer or plastic resin (the terms “plastic” and “polymer” are used herein synonymously and interchangeably) material, a feed screw with a helical flight or flights on its outer surface rotates in a heated containment barrel. Plastic pellets are fed into the apparatus at one end and the application of heat, friction, and shear forces to the pellets melts and mixes the pellets into a polymer shot (or volume) suitable for injection. The screw then is reciprocated (moved forward), closing a non-return valve, and acts as a plunger to inject the shot of plastic into a mold.
In injection molding (and to a lesser extent, extrusion) a wide variety of plastic formulations may be processed using the same injection molding apparatus. There are numerous screw designs adapted to achieve various characteristics during melting and mixing. Different screws may be used that are optimized for the particular plastic formulation being processed. The suitability (or lack thereof) of a particular screw design for the particular plastic formulation it processes can have significant impact on the quality of the resulting part and the defect rate in manufacturing those parts.
A need exists for screw designs that maximize the versatility of the screw for use with various plastic formulations.